Heat transfer enhancement by a focused ultrasound field

A focused ultrasound field is set up in a heat transfer cavity with an elliptical cross section. A sound source and a heat source are designed at the two focus points where the sound intensity is reinforced based on the interference and standing wave criteria. The sound intensities and heat transfer coefficients of the cavity with a focused ultrasonic field and an ordinary cavity with a rectangular cross section are measured under the natural convection heat transfer regime. The distribution of the heat transfer coefficient matches the distribution of the sound intensity. The heat transfer performance is then enhanced in the cavity with a focused ultrasonic field. The cavitations and acoustic streaming characteristics in the cavity with a focused ultrasonic field and the ordinary cavity are also studied. The velocity of acoustic streaming is larger in the cavity with a focused ultrasonic field than in the ordinary cavity, and no cavitation is observed in the ordinary cavity. Although the cavitation cloud around the heat source is unfavorable for the heat transfer in the cavity with a focused ultrasonic field, the cavitations collapse and the resulting high temperature, higher pressure, and microjet effects still contribute substantially to heat transfer.